Hydrostatic, uniaxial, and triaxial compression tests on unpoled "Chem-prep" PZT 95/5-2Nb ceramic within temperature range of -55 to 75 degrees C.

Abstract

Sandia is currently developing a lead-zirconate-titanate ceramic 95/5-2Nb (or PNZT) from chemically prepared ("chem-prep") precursor powders. Previous PNZT ceramic was fabricated from the powders prepared using a "mixed-oxide" process. The specimens of unpoled PNZT ceramic from batch HF803 were tested under hydrostatic, uniaxial, and constant stress difference loading conditions within the temperature range of -55 to 75°C and pressures to 500 MPa. The objective of this experimental study was to obtain mechanical properties and phase relationships so that the grain-scale modeling effort can develop and test its models and codes using realistic parameters. The stress-strain behavior of "chem-prep" iv PNZT under different loading paths was found to be similar to that of "mixed-oxide" PNZT. The phase transformation from ferroelectric to antiferroelectric occurs in unpoled ceramic with abrupt increase in volumetric strain of about 0.7 % when the maximum compressive stress, regardless of loading paths, equals the hydrostatic pressure at which the transformation otherwise takes place. The stress-volumetric strain relationship of the ceramic undergoing a phase transformation was analyzed quantitatively using a linear regression analysis. The pressure (P T1 H ) required for the onset of phase transformation with respect to temperature is represented by the best-fit line, P T1 H (MPa) = 227 + 0.76 T (°C). We also confirmed that increasing shear stress lowers the mean stress and the volumetric strain required to trigger phase transformation. At the lower bound (-55°C) of the tested temperature range, the phase transformation is permanent and irreversible. However, at the upper bound (75°C), the phase transformation is completely reversible as the stress causing phase transformation is removed.v ACKNOWLEDGEMENTS